The Shallow Marine Succession of Begrih Formation (Pliocene), Mukah Area, Sarawak: Facies, Stratigraphic Characteristics, and Paleoenvironmental Interpretation

Abstract

This work presents the detailed facies analysis of the Begrih Formation exposed along the Mukah–Selangau road, Sarawak, East Malaysia. The Begrih Formation shows a variety of sedimentary facies in terms of composition, sedimentary structures, bed geometry, and microfossils. Fifteen sedimentary facies from seven (07) outcrops of Begrih Formation have been identified and interpreted. These sedimentary facies are categorized into three main types depending on the major lithology type. (1) Mud-dominated unit: laminated mudstone/shale (Msl), mudstone with planer and lenticular sandstone/siltstone laminations (Mpl), and fossiliferous mudstone (Mf); (2) Sandstone/Siltstone-dominated facies: trough cross-stratified sandstone (Sts), planar-laminated sandstone and mudstone (Slm), rhythmically bedded sandstone and mudstone (Srh), hummocky cross-stratified sandstone (Shs), hummocky-stratified sandstone with mudstone (Shsm), ripple-laminated sandstone and mudstone (Srp), flaser-bedded sandstone (Sfl), and bioturbated sandstone (Sb); and (3) Conglomerate: massive conglomerates (Gm), trough cross-bedded pebbly conglomerate (Gpt), bioturbated conglomerate (Gb), and coal facies. These fifteen facies are grouped into seven facies association; (1) Shelf and lower offshore, (2) Upper offshore, (3) Lower to middle shoreface, (4) Upper shoreface, (5) Foreshore, (6) Lagoonal facies, and (7) Backshore/fluvial facies. The pattern of facies and presence of distinct foraminifera species imply that these facies were deposited in the shallow marine setting with pronounced storms, wave, fluvial, and tidal influence along the paleo-margin.